The heat arising during slip on lamellae and/or friction disks, which transmit torque, is dissipated in liquid-cooled friction clutches using coolant liquid. This coolant liquid, which may be used simultaneously for lubricating bearings of the clutch or even of a transmission, circulates in a loop, within which it flows through a cooler. It is expedient to regulate the quantity of coolant liquid supplied to the clutch and flowing between the friction disks depending on the driving condition. During driving, a minimum volume flow is required to dissipate the heat arising during slip regulation. When the clutch is put in, a larger volume flow must be provided, since a larger quantity of heat arises. During synchronization, the volume flow is to be significantly reduced in order to avoid a residual drag torque on the clutch lamellae and/or friction disks and thus on the corresponding synchronization unit. In addition, the coolant liquid system must be capable of independently starting a coolant loop after the engine is started.
In EP 11 74 633 A2, from which the preambles of the independent claims proceed, a liquid-cooled friction clutch is known, in which coolant liquid, which rotates and/or revolves together with the interior of the rotating clutch housing after flowing radially through the lamellar packet and from there is removed by fixed blades first in the axial direction and then radially inward and is supplied to an oil sump of a transmission adjoining the clutch, is supplied radially within the lamellae and/or friction disks from a transmission-side attachment. In this way, coolant liquid introduced into the interior and/or wet chamber of the clutch may be returned unpressurized, so that the fill level of the coolant liquid is adjustable in such a way that the clutch lamellae are not permanently immersed in coolant liquid and drag torques are avoided. The returned coolant liquid is recirculated with the aid of a pump and resupplied to the clutch radially inside the friction disks.